(1) Field of the Invention
The present invention relates generally to the field of coatings compositions generally classified in class 106 and/or class 428 of the U.S. Pat. and Trademark Office classification system.
This application relates to the general field of co-pending U.S. Ser. No. 382,853 filed May 24, 1982, now abandoned.
(2) Description of the Prior Art
The known art for drying or curing resins including principally alkyd resins comprises metal-catalyzed oxidation reactions through the unsaturation of the body of the resin polymer. These conventional types of drying agents have been used for many years and the research is voluminous on this subject. The oxidative process is very useful and produces most of the alkyd coatings used commercially today. However, the oxidative process has always been limited by the concentration of the unsaturation of the resin polymer. Therefore, a very long or long oil type alkyd (e.g. produced using more than 60% by weight of the fatty acid oil) could not be satisfactorily cured by the oxidative method. Even medium length alkyd polymers are hindered by the oxidative curing process because of the time required and the heat energy and heating apparatus necessary to shorten the cure time to meet commercial production schedules. The higher molecular weight alkyd resins of the very long to medium long oil types are conventionally caused to dry by cross linking them by the addition of melamine type driers and/or substitution of urea-formaldehyde type resins. Such formulations also require high energy levels for cure and involve up to several minutes of dwell time in the oven (e.g. 10 minutes at about 400.degree. F. to 7 days at temperatures of 200.degree. F.). These melamine and urea-formaldehyde cured alkyd systems also give off toxic formaldehyde.
In contrast, the present carbodiimide driers become totally a part of the alkyd resin and the systems of the present invention do not produce odors, fumes, or evolution of toxic or corrosive substances through the atmosphere, other than the natural evaporation of whatever solvent is chosen for use with the system of the invention.
The literature contains many teachings of preparation of carbodiimides and polycarbodiimides.
U.S. Pat. No. 3,755,242 to Reich (Class 524, subclass 437) teaches preparation of isocyanade-terminated high molecular weight polycarbodiimides.
U.S. Pat. No. 3,450,669 to Nolen (Class 524, subclass 133) teaches use of carbodiimides as a stabilizer for polyesters, polyethers and polymethanes.
U.S. Pat. No. 2,430,479 to Pratt et al (Class 154, subclass 140) teaches the use of polycarbodiimides as adhesives and adhesive modifiers.
It is known that many carbodiimides and polycarbodiimides moieties are formed in the production of copolymer foams utilizing the reaction of organic polyiscyanurates with polycarboxilic compounds.
U.S. Pat. No. 3,644,234 to Grieve (Class 260, subclass 2.5) and U.S. Pat. No. 3,723,364 to McLaughlin et al (Class 521, subclass 157) teach the above production of copolymer foams.
U.S. Pat. No. 4,118,536 to Beardsley et al (Class 427, subclass 385) teaches the use of carboxidiimides as primers and as ingredients in composite coatings.
West German DT-OS No. 2,655,836 now U.S. Pat. No. 4,060,664 (assigned 3M), class 156, subclass 331.1 discloses a novel adhesive composite coating wherein the intermediate layer is comprised of polymeric polycarbodiimides.
U.S. Pat. No. 3,556,829 to Gebura (CLass 106, subclass 288) discloses the use of carbodiimides to modify clays used in coating manufacturing.
U.S. Pat. No. 3,619,236 to Dappen et al (Class 430, subclass 621) teaches use of carbodiimides with gelatin and carboxyl-containing polymers as a support to provide photographic materials of improved dimensional stability.
All of the above references show the benefits of the carbodiimide moieties in coatings of many different types. However, none of these references teaches or suggests that the carbodiimides, polycarbodiimides or substituted carbodiimides are excellent driers for alkyd resins, polyesters, polyacrylate-type polymers or any of the resins or polymers that contain carboxylate groups having at least one active (labile) hydrogen molecule.
The driers of the present invention provide cross-linking for the alkyd type resins, polyesters, polyacrylates, modified vinyl-acrylics, epoxides, urethanes and polyurethanes, metal salts, e.g., Ca, Co, Cu, Pb, Mn, Ti, Zr, salts of acids and the melamines, urea-formaldehyde, aziridines and peroxides are the most conventional driers presently used. All of these conventional driers have some disadvantages; the metal salts in many cases cause slow drying, require heat or combination of long drying time plus heat to obtain thorough cure or drying. The melamine types all give off formaldehyde and most require relatively long curing periods at ambient temperatures. The aziridines are toxic and hydrolize easily in water systems and have relatively short shelf life or storage time. The organic peroxides are hazardous and require special handling and storage and only work for a free-radical polymerization. The urea formaldehyde types require high energy for cure and give off formaldehyde during cure.
In contrast, the carbodiimides, polycarbodiimides and substituted carbodiimides of the present invention avoid all of the above disadvantages.
From the above review of the art, it is apparent that the driers and cross-linking agents conventionally used today do not produce finished products with all the properties desired. Many attempts have been made to dry alkyd resins at ambient room temperature in relatively short periods of time. Those familiar with the art know that new driers are needed that will cause the alkyd resins to harden and present water resistance in a short time. The carbodiimides and related compounds described in this invention impart those desired properties to the alkyd polymers and copolymers.